Various single cell organisms, including bacteria, yeasts and microalgae, are used for various purposes in the agricultural, livestock farming, marine fisheries, medicinal and resources fields. For example, bacteria and yeasts are widely used for the expression of medicinal proteins. Particularly, microalgae have the capability to produce a large amount of neutral lipids, which can be converted to biodiesel, from photoenergy, carbon dioxide and inorganic materials, and thus have recently received attention as an alternative that can solve the energy resources exhaustion problem resulting from a rapid increase in the use of fossil fuels and the global warming problem resulting from greenhouse gas emissions.
Microalgae contain pigments such as chlorophyll, carotinoids and phycobilins, and are single cell algae that can grow through photosynthesis and can synthesize organic materials required for photosynthesis. Most phytoplanktons belong to microalgae. It has been reported to date that more than hundreds of thousands of species of microalgae are present in freshwater and marine ecosystems, and research and development has been performed for various purposes. Due to limitations on genetic manipulation, there is much difficulty in improving strains to increase productivity.
For the efficient use of such microalgae, the development of an optimal strain suitable for purposes, the optimization of media, the design of an optimal reactor, studies on metabolic processes and product purification, etc., are required.
One of methods for developing an optimal strain comprises inducing specific or random mutation in the genome of microalgae, and identifying a strain showing desired properties, for example, increased photosynthetic efficiency, high lipid production or rapid growth rate.
U.S. Patent Publication No. 2008-00254493 is directed to a method for screening a mutant microbial strain that does not express protease, and discloses a method comprising culturing mutation-induced strains on a gel containing a protease substrate, and identifying a mutant strain based on whether the substrate was degraded.
Korean Patent Laid-Open Publication No. 2011-0018798 is directed to a microfluidic cell chip, a method of quantitatively analyzing cell death using the same, and a system of analyzing a cell image using the same, and discloses a system and method capable of analyzing and imaging cell death in real time using a microfluidic system.
However, in many cases, it is required to perform screening of tens of thousands of strains, which requires complex biochemical and molecular biological analysis. Thus, it is required to develop a method capable of high-throughput screening of strains in the initial stage of screening.
Accordingly, the present inventors have made extensive efforts to solve the above-described problem and develop a method for efficiently screening single cell organisms, and as a result, have found that improved single cell organisms can be effectively screened using a microfluidic photoreaction system based on phototaxis, thereby completing the present invention.